1. Field of the Invention
The present invention relates to an arrangement in regulating valves for steam, gases or liquids, and includes a cage fixedly disposed in a valve housing. A movable valve body is disposed in the cage for connection, via a spindle, to a setting means having a position regulator for positional setting of the valve body in the cage. The body is provided at its lower portion with a sealing surface for enabling sealing engagement against a seating on the valve housing. The body in its movement to its upper, or completely open, position successively uncovers orifices in the fixed cage so as to achieve a gradual increase in the through-flow area of the valve.
2. Description of the Related Art
Regulating valves on the market at present have a fixed cage and a movable valve body, which is abruptly cut off below the sealing surface, thus providing a valve characteristic of the type signifying quick opening for small opening increments. The cause of this is that leakage via the gap between fixed cage and movable body is considerable, with consequential difficulty in accurately regulating small flows. For purely technical reasons, it is not possible to have small clearances between the fixed cage and valve body. The cage is namely subjected to pressure on its outside, particularly when the medium to be regulated is superheated steam, which may have a temperature of 540.degree. C., for example. Since the cage will then be caused to contract, the clearance between cage and valve body must be relatively large to avoid sticking or seizure of the body in the cage during the operational life for which the valve has been designed.